LTC4015 Ready to charge but Charge suspended

Some additional details:

There is also some problems with the I2C communication whenever VIN goes too low, below 14-15V, particularily with a good battery connected. Above or without a battery connected, communication is mostly good with occasional dropouts.

The circuit is powered by a benchtop PSU and feeds a fairly large 12V sealed lead-acid battery.

We are using the following MOSFETs:

M1, M2, M3: NTMFS5C670NL (60 V, 6.1mΩ, 71A, VGS(th) max. 2V)

M4: IPD50P04P4L-11 (-40V, 10.6mΩ, -50 A, VGS(th) max. -2.2V)

Some measured voltages as near to or on the LTC4015 as possible:

VIN: 18.35V

IntVCC: 4.05V

InFET: 20.06V

OutFET 18.32V

BG: 0,02 mV

TG: 12.41V

2P5Vcc: 2.49V

Sys: 18.33V

CSP: 12.54V

CSPm5: 7.66V

CLP: 18.33V

3V3: 3.31V

UVclb: 600.9mV

CCRefp: 12.54V

CCRefm: 12.17V

Batsens: 12.54V

NTCbias: 147mV

VC: 0.53mV

It seems when I connect a busted lead acid battery that the charger tries to pull OutFET as I can hear clicking in the inductor, but when a good battery is connected as in the case above, it does not appear to try charging at all.

Some SMBUS data:

I (708138) batt: LTC4015_NTC_PAUSE_BF: 0
I (708158) batt: LTC4015_TIMER_TERM_BF: 0
I (708178) batt: LTC4015_CHARGER_ENABLED_BF: 0
I (708198) batt: LTC4015_MPPT_EN_PIN_BF: 1
I (708218) batt: LTC4015_CHARGER_SUSPENDED_BF: 1
I (708238) batt: LTC4015_CHARGER_STATE_ALERTS: 0
I (708258) batt: LTC4015_CHARGER_STATE: 256 (100000000)
I (708278) batt: LTC4015_LIMIT_ALERTS: 0
I (708298) batt: LTC4015_CHARGE_STATUS_ALERTS: 0
I (708318) batt: LTC4015_SYSTEM_STATUS: 2759 (101011000111)
I (708338) batt: LTC4015_EQUALIZE_REQ_BF: 0
I (708358) batt: LTC4015_DRVCC_GOOD_BF: 1
I (708378) batt: LTC4015_CELL_COUNT_ERROR_BF: 0
I (708398) batt: LTC4015_OK_TO_CHARGE_BF: 1
I (708418) batt: LTC4015_NO_RT_BF: 0
I (708438) batt: LTC4015_THERMAL_SHUTDOWN_BF: 0
I (708458) batt: LTC4015_VIN_OVLO_BF: 0
I (708478) batt: LTC4015_VIN_GT_VBAT_BF: 1
I (708498) batt: LTC4015_ABSORB_TIMER: 0
I (708518) batt: LTC4015_EQUALIZE_TIMER: 0
I (708538) batt: LTC4015_C_OVER_X_TERM_BF: 0
I (708558) batt: LTC4015_VIN_UVCL_ACTIVE_BF: 0
I (708578) batt: LTC4015_IIN_LIMIT_ACTIVE_BF: 0
I (708598) batt: LTC4015_CONSTANT_CURRENT_BF: 0
I (708618) batt: LTC4015_CONSTANT_VOLTAGE_BF: 0
I (708638) batt: LTC4015_CHEM_BF: 8
I (708658) batt: LTC4015_CELL_COUNT_PINS_BF: 6
I (708678) batt: LTC4015_MEAS_SYS_VALID: 1
I (708698) batt: LTC4015_IIN_LIMIT_SETTING: 10.67 A
I (708718) batt: LTC4015_ICHARGE_TARGET_BF: 10.67 A
I (708738) batt: LTC4015_VCHARGE_SETTING: 2.20 V/cell (13.20 V/tot)
I (708758) batt: LTC4015_IBAT: 0.00 μA (0.00 mA)
I (708778) batt: LTC4015_VBAT: 2085936.22 μV (2085.94 mV)
I (708798) batt: LTC4015_VBAT_FILT: 11.12 mV
I (708818) batt: LTC4015_VSYS: 18.2862 V
I (708838) batt: LTC4015_VIN: 18.3389 V
I (708858) batt: LTC4015_IIN: 0.0000 mA
I (708878) batt: LTC4015_DIE_TEMP: 34.76 °C
I (708898) batt: LTC4015_NTC_RATIO: 10037.61 ohm
I (708918) batt: LTC4015_BSR: 0.00 ohm
I (708938) batt: LTC4015_QCOUNT: 32768 C

IBAT and IIN do show values most of the time, but there is a bit of intermittency, this is just cut from a random reporting cycle.

Hi all, I sent you both friend requests. You can privately message me your KiCad project or gerbers so I can look at the layout.

Let's keep the discussion public to help others, though.

Regards,

Zack

We're working with the theory at the moment that our issues are caused by a too long high speed switching path, with too poor connection to ground as the symptoms seem to fit a previous poster. Primarily for the switching path, our C1 was quite far from the other components.

We've tried to make a new outlay rectifying these two issues, so if you agree this is the likely culprit I will order up a test batch of these and give them a try.

Best regards,

Preben

If you have time to take a quick look at the latest revision we sent we would very much appreciate it as we are behind in our schedule, and have to get a new testbatch out on monday. It would be great to have some feedback so as to not risk another setback. Best regards Preben

Hi Preben, I have given you some feedback.